[SettingsProvider] fix caching of Global settings on non-system users

Global settings are shared across users, so all users should share the
same generation tracking cache for Global settings.

BUG: 272251616
BUG: 228619157
Test: atest android.accessibilityservice.cts.AccessibilityWindowReportingTest#testDisableWindowAnimations
Change-Id: I933fa0b8a1687f26c907b96e741433b165037748